Nadph structural formula. Biological functions

SPECTRAL ANALYSIS(using emission spectra) is used in almost all sectors of the economy. Widely used in the metal industry for the rapid analysis of iron, steel, cast iron, as well as various special steels and finished metal products, to determine the purity of light, non-ferrous and precious metals. Great Application has spectral analysis in geochemistry in the study of the composition of minerals. IN chemical industry and related industries, spectral analysis serves to establish the purity of manufactured and used products, to analyze catalysts, various residues, sediments, turbidities and wash waters; in medicine - for the discovery of metals in various organic tissues. A number of special problems that are difficult to solve or cannot be solved in any other way are solved using spectral analysis quickly and accurately. This includes, for example, the distribution of metals in alloys, the study of sulfide and other inclusions in alloys and minerals; This type of research is sometimes referred to as local analysis.

The choice of one or another type of spectral apparatus from the point of view of the sufficiency of its dispersion is made depending on the purpose and objectives of spectral analysis. Quartz spectrographs with greater dispersion, giving for wavelengths 4000-2200 Ӑ a strip of spectrum at least 22 cm long. For other elements it may be Apparatuses are used that produce spectra 7-15 cm long. Spectrographs with glass optics are generally of less importance. Of these, combined instruments are convenient (for example, from the companies of Hilger and Fuss), which, if desired, can be used as a spectroscope and spectrograph. The following energy sources are used to obtain spectra. 1) Flame of burning mixture- hydrogen and oxygen, a mixture of oxygen and illuminating gas, a mixture of oxygen and acetylene, or finally air and acetylene. In the latter case, the temperature of the light source reaches 2500-3000°C. The flame is most suitable for obtaining spectra of alkali and alkaline earth metals, as well as for elements such as Cu, Hg and Tl. 2) Voltaic arc. a) Ordinary, ch. arr. direct current, with a force of 5-20 A. It is used with great success for qualitative analysis difficult to fuse minerals that are introduced into the arc in the form of pieces or finely ground powders. For the quantitative analysis of metals, the use of a conventional voltaic arc has a very significant drawback, namely, that the surface of the analyzed metals is covered with an oxide film and the arc combustion ultimately becomes uneven. The temperature of the voltaic arc reaches 5000-6000°C. b) Intermittent arc (Abreissbogen) of direct current with a power of 2-5 A at a voltage of about 80 V. Using special device arc burning is interrupted 4-10 times per second. This method of excitation reduces oxidation of the surface of the analyzed metals. At higher voltages - up to 220 V and a current of 1-2 A - an intermittent arc can also be used for analyzing solutions. 3) Spark discharges, obtained using an induction coil or, more often, a direct or (preferably) alternating current transformer with a power of up to 1 kW, giving 10,000-30,000 V in the secondary circuit. Three types of discharges are used, a) Spark discharges without capacitance and inductance in the secondary circuit, called sometimes in an arc high voltage(Hochspannungsbogen). The analysis of liquids and molten salts using such discharges is highly sensitive. b) Spark discharges with capacitance and inductance in the secondary circuit, often also called condensed sparks, represent a more universal energy source, suitable for exciting the spectra of almost all elements (except alkali metals), as well as gases. The connection diagram is shown in Fig. 1,

where R is the rheostat in the primary circuit, Tr is the alternating current transformer, C 1 is the capacitance in the secondary circuit I, S is the switch for changing the inductance L 1, U is the synchronous breaker, LF is the spark arrester, F is the working spark gap. The secondary circuit II is tuned into resonance with the secondary circuit I using inductance and variable capacitance C 2; a sign of the presence of resonance is greatest strength current, shown by milliammeter A. The purpose of the secondary circuit II of the synchronous breaker U and the spark arrester LF is to make electrical discharges as uniform as possible both in character and in number over a certain period of time; during normal work such additional devices are not introduced.

When studying metals in the secondary circuit, a capacitance of 6000-15000 cm3 and an inductance of up to 0.05-0.01 N are used. To analyze liquids, a water rheostat with a resistance of up to 40000 Ohms is sometimes introduced into the secondary circuit. Gases are studied without inductance with a small capacitance. c) Tesla current discharges, which are carried out using the circuit shown in Fig. 2,

where V is a voltmeter, A is an ammeter, T is a transformer, C is a capacitance, T-T is a Tesla transformer, F is the spark gap where the analyzed substance is introduced. Tesla currents are used to study substances that have a low melting point: various plant and organic preparations, deposits on filters, etc. In the spectral analysis of metals, in the case of a large number of them, they usually themselves are electrodes, and they are given some form, for example, from those shown in FIGS. 3,

where a is an electrode made from the thick wire being analyzed, b is from tin, c is a bent thin wire, d is a disk cut from a thick cylindrical rod, e is a shape cut from large pieces casting In quantitative analysis, it is always necessary to have the same shape and size of the electrode surface exposed to sparks. If the amount of metal being analyzed is small, you can use a frame made of some pure metal, for example, gold and platinum, in which the analyzed metal is fixed, as shown in Fig. 4.

Quite a few methods have been proposed for introducing solutions into a light source. When working with a flame, a Lundegaard atomizer is used, schematically shown in Fig. 5 together with a special burner.

The air blown through the BC sprayer captures the test liquid, poured in an amount of 3-10 cm 3 into recess C, and carries it in the form of fine dust to burner A, where it is mixed with gas. To introduce solutions into the arc, as well as into the spark, clean carbon or graphite electrodes are used, on one of which a recess is made. It should be noted, however, that it is very difficult to cook coals completely clean. The methods used for cleaning - alternate boiling in hydrochloric and hydrofluoric acids, as well as calcination in a hydrogen atmosphere to 2500-3000 ° C - do not produce coals free of impurities; Ca, Mg, V, Ti, Al remain (albeit traces), Fe, Si, B. Coals of satisfactory purity are also obtained by calcining them in air using an electric current: a current of about 400 A is passed through a carbon rod with a diameter of 5 mm, and the strong incandescence achieved in this way (up to 3,000 ° C) is sufficient for so that within a few seconds most of the impurities contaminating the coals will evaporate. There are also methods for introducing solutions into a spark, where the solution itself is the lower electrode, and the spark jumps to its surface; another electrode can be any pure metal. An example of such a device is shown in Fig. 6 Gerlyach liquid electrode.

The recess into which the test solution is poured is lined with platinum foil or covered with a thick layer of gold. In fig. 7 shows a Hitchen apparatus, which also serves to introduce solutions into a spark.

From vessel A, the test solution flows in a weak stream through tube B and quartz nozzle C into the sphere of action of spark discharges. The lower electrode, soldered into a glass tube, is attached to the apparatus using a rubber tube E. The attachment C, shown in Fig. 7 separately, has a cutout on one side for mortar walling. D - glass safety vessel in which a round hole is made for exit ultraviolet rays. It is more convenient to make this vessel quartz without a hole. The top electrode F, graphite, carbon or metal, is also fitted with a splash-proof plate. For a “high-voltage arc” that strongly heats the analyzed substances, Gerlach uses cooled electrodes when working with solutions, as shown schematically in Fig. 8.

A glass funnel G is attached to a thick wire (6 mm in diameter) using a stopper K, into which pieces of ice are placed. At the upper end of the wire, a round iron electrode E with a diameter of 4 cm and a height of 4 cm is fixed, on which a platinum cup P is placed; the latter should be easily removable for cleaning. The top electrode should also be used. thick to avoid melting. When analyzing small quantities of substances - sediments on filters, various powders, etc. - you can use the device shown in Fig. 9.

A lump is made from the test substance and filter paper, moistened for better conductivity with a solution, for example, NaCl, placed on the lower electrode, sometimes consisting of pure cadmium, enclosed in a quartz (worse glass) tube; the top electrode is also some pure metal. For the same analyzes when working with Tesla currents, a special spark gap design is used, shown in Fig. 10 a and b.

In the round hinge K, an aluminum plate E is fixed in the desired position, on which a glass plate G is placed, and on the latter - preparation P on filter paper F. The preparation is moistened with some acid or salt solution. This entire system is a small capacitor. To study gases, closed glass or quartz vessels are used (Fig. 11).

For quantitative analysis of gases, it is convenient to use gold or platinum electrodes, the lines of which can be used for comparison. Almost all of the above-mentioned devices for introducing substances into a spark and arc are mounted in special stands during operation. An example is the Gramont tripod shown in Fig. 12:

using screw D, the electrodes are simultaneously moved apart and moved apart; screw E is used to move the upper electrode parallel to the optical bench, and screw C is for lateral rotation of the lower electrode; screw B is used for lateral rotation of the entire upper part of the tripod; finally, using screw A, you can raise or lower the entire top part tripod; N - stand for burners, glasses, etc. The choice of energy source for a particular research purpose can be made based on the following approximate table.

Qualitative analysis. In qualitative spectral analysis, the discovery of an element depends on many factors: the nature of the element being determined, the energy source, the resolution of the spectral apparatus, as well as the sensitivity of photographic plates. Regarding the sensitivity of the assay, the following guidelines can be made. When working with spark discharges in solutions, you can open 10 -9 -10 -3%, and in metals 10 -2 -10 -4% of the element under study; when working with a voltaic arc, the opening limits are about 10 -3%. The absolute amount that can be open when working with a flame, is 10 -4 -10 -7 g, and with spark discharges 10 -6 -10 -8 g of the element under study. The greatest sensitivity of discovery applies to metals and metalloids - B, P, C; less sensitivity for metalloids As, Se and Te; halogens, as well as S, O, N in their compounds, cannot be used at all. open and m.b. discovered only in some cases in gas mixtures.

For qualitative analysis highest value have “last lines”, and when analyzing the task is to most precise definition wavelengths of spectral lines. In visual studies, wavelengths are measured along the spectrometer drum; these measurements can be considered only approximate, since the accuracy is usually ±(2-З)Ӑ and in the Kaiser tables this error interval can correspond to about 10 spectral lines belonging to different elements for λ 6000 and 5000Ӑ and about 20 spectral lines for λ ≈ 4000 Ӑ. The wavelength is determined much more accurately by spectrographic analysis. In this case, on the spectrograms, using a measuring microscope, the distance between the lines with known length waves and defined; Hartmann's formula is used to find the wavelength of the latter. The accuracy of such measurements when working with an instrument that produces a spectrum strip about 20 cm long is ± 0.5 Ӑ for λ ≈ 4000 Ӑ, ± 0.2 Ӑ for λ ≈ 3000 Ӑ and ± 0.1 Ӑ for λ ≈ 2500 Ӑ. The corresponding element is found in the tables based on the wavelength. The distance between lines during normal work is measured with an accuracy of 0.05-0.01 mm. This technique is sometimes conveniently combined with shooting spectra with so-called Hartmann shutters, two types of which are shown in Fig. 13, a and b; With their help, the spectrograph slit can be made of different heights. Fig. 13c schematically depicts the case of qualitative analysis of substance X - the identification of elements A and B in it. The spectra of FIG. 13, d show that in substance Y, in addition to element A, the lines of which are designated by the letter G, there is an impurity, the lines of which are designated z. Using this technique, in simple cases, you can perform a qualitative analysis without resorting to measuring the distances between lines.

Quantitative Analysis. For quantitative spectral analysis, lines that have the greatest possible concentration sensitivity dI/dK are of greatest importance, where I is the intensity of the line, and K is the concentration of the element giving it. The greater the concentration sensitivity, the more precise analysis. Over time developed whole line methods of quantitative spectral analysis. These methods are as follows.

I. Spectroscopic methods(without photography) almost all are photometric methods. These include: 1) Barratt method. At the same time, the spectra of two substances are excited - the test and the standard - visible in the field of view of the spectroscope side by side, one above the other. The path of the rays is shown in Fig. 14,

where F 1 and F 2 are two spark gaps, the light from which passes through Nicolas prisms N 1 and N 2, polarizing the rays in mutually perpendicular planes. Using prism D, the rays enter the slit S of the spectroscope. A third Nicolas prism, an analyzer, is placed in its telescope, rotating which achieves the same intensity of the two lines being compared. Previously, when studying standards, i.e. substances with known contents of elements, the relationship between the angle of rotation of the analyzer and the concentration is established, and a diagram is drawn from this data. When analyzing by the angle of rotation of the analyzer, the desired value is found from this diagram percentage. The accuracy of the method is ±10%. 2) . The principle of the method is that light rays after the spectroscope prism pass through a Wollaston prism, where they diverge into two beams and are polarized in mutually perpendicular planes. The ray path diagram is shown in Fig. 15,

where S is the slit, P is the spectroscope prism, W is the Wollaston prism. In the field of view, two spectra B 1 and B 2 are obtained, lying next to each other; L - magnifying glass, N - analyzer. If you rotate the Wollaston prism, the spectra will move relative to each other, which allows you to combine any two of their lines. For example, if iron containing vanadium is analyzed, then the vanadium line is combined with some nearby single-color iron line; then, by turning the analyzer, they achieve the same brightness of these lines. The angle of rotation of the analyzer, as in the previous method, is a measure of the concentration of the desired element. The method is especially suitable for the analysis of iron, the spectrum of which has many lines, which makes it possible to always find lines suitable for research. The accuracy of the method is ± (3-7)%. 3) Occhialini method. If the electrodes (for example, the metals being analyzed) are placed horizontally and the image is projected from a light source onto the vertical slit of the spectroscope, then both during spark and arc discharges, lines of impurities may appear. open depending on the concentration at a greater or lesser distance from the electrodes. The light source is projected onto the slit using special lens equipped with a micrometric screw. During analysis, this lens moves and the image of the light source moves along with it until any impurity line in the spectrum disappears. The measure of impurity concentration is the reading on the lens scale. Currently, this method has also been developed for working with the ultraviolet part of the spectrum. It should be noted that Lockyer used the same method of illuminating the slit of a spectral apparatus and he developed a method of quantitative spectral analysis, the so-called. "long and short lines" method. 4) Direct photometry of spectra. The methods described above are called visual. Instead of visual studies, Lundegaard used a photocell to measure the intensity of spectral lines. The accuracy of determining alkali metals when working with a flame reached ± 5%. For spark discharges, this method is not applicable, since they are less constant than flames. There are also methods based on changing the inductance in the secondary circuit, as well as using artificial attenuation of the light entering the spectroscope until the spectral lines under study disappear in the field of view.

II. Spectrographic methods. With these methods, photographic photographs of spectra are examined, and the measure of the intensity of the spectral lines is the blackening they produce on the photographic plate. The intensity is assessed either by eye or photometrically.

A. Methods without photometry. 1) Last lines method. When the concentration of any element in the spectrum changes, the number of its lines changes, which makes it possible, under constant operating conditions, to judge the concentration of the element being determined. A series of spectra of substances with a known content of the component of interest are photographed, the number of its lines is determined on the spectrograms, and tables are compiled indicating which lines are visible at given concentrations. These tables further serve for analytical definitions. When analyzing the spectrogram, the number of lines of the element of interest is determined and the percentage content is found from the tables, and the method does not give an unambiguous figure, but concentration limits, i.e. “from-to”. It is most reliably possible to distinguish concentrations that differ from each other by a factor of 10, for example, from 0.001 to 0.01%, from 0.01 to 0.1%, etc. Analytical tables are important only for very specific operating conditions, which may vary greatly between laboratories; In addition, careful adherence to constant working conditions is required. 2) Comparative spectra method. Several spectra of the analyzed substance A + x% B are photographed, in which the content of x element B is determined, and in the intervals between them on the same photographic plate - spectra of standard substances A + a% B, A + b% B, A + c% B , where a, b, c are the known percentage of B. In the spectrograms, the intensity of the B lines determines between which concentrations the value of x lies. The criterion for the constancy of operating conditions is the equality of the intensity in all spectrograms of any nearby line A. When analyzing solutions, it is added to them the same number any element that produces a line close to lines B, and then the constancy of operating conditions is judged by the equality of the intensity of these lines. How less difference between concentrations a, b, c, ... and the more accurately the equality of the intensity of lines A is achieved, the more accurate the analysis. A. Rice, for example, used concentrations of a, b, c, ..., related to each other, as 1: 1.5. Adjacent to the method of comparative spectra is the method of “selection of concentrations” (Testverfahren) according to Güttig and Thurnwald, which is applicable only to the analysis of solutions. It lies in the fact that if in two solutions containing a% A and x% A (x is greater or less than a), which can now be determined from their spectra, then such an amount n of the element A is added to any of these solutions so that the intensity of its lines in both spectra becomes the same. This will determine the concentration x, which will be equal to (a ± n)%. You can also add some other element B to the analyzed solution until the intensities of certain lines A and B are equal and, based on the amount of B, estimate the content of A. 3) Homologous pair method. In the spectrum of a substance A + a% B, the lines of elements A and B are not equally intense and, if there are a sufficient number of these lines, you can find two such lines A and B, the intensity of which will be the same. For another composition A + b% B, other lines A and B will be equal in intensity, etc. These two identical lines are called homologous pairs. The concentrations of B at which one or another homologous pair occurs are called fixing points this couple. To work using this method, preliminary compilation of tables of homologous pairs using substances of known composition is required. How more complete table, i.e., the more they contain homologous pairs with fixing points that differ as much as possible less friend from each other, the more accurate the analysis. Quite a few of these tables have been compiled a large number of, and they can be used in any laboratory, since the conditions of the discharges during their preparation are precisely known and these conditions can be used. absolutely accurately reproduced. This is achieved using the following simple trick. In the spectrum of substance A + a% B, two lines of element A are selected, the intensity of which varies greatly depending on the value of self-induction in the secondary circuit, namely one arc line (belonging to the neutral atom) and one spark line (belonging to the ion). These two lines are called fixing pair. By selecting the value of self-inductance, the lines of this pair are made identical and the compilation is carried out precisely under these conditions, always indicated in the tables. Under the same conditions, the analysis is carried out, and the percentage is determined based on the implementation of one or another homologous pair. There are several modifications of the homologous pair method. Of these, the most important is the method auxiliary spectrum, used in the case when elements A and B do not have sufficient quantity lines. In this case, the spectral lines of element A are connected in a certain way with the lines of another, more suitable element G, and the role of A begins to be played by element G. The method of homological pairs was developed by Gerlyach and Schweitzer. It is applicable to both alloys and solutions. Its accuracy is on average about ±10%.

IN. Methods using photometry. 1) Barratt method. Fig. 16 gives an idea of the method.

F 1 and F 2 are two spark gaps, with the help of which the spectra of the standard and the analyzed substance are simultaneously excited. Light passes through 2 rotating sectors S 1 and S 2 and, with the help of a prism D, forms spectra that are located one above the other. By selecting sector cuts, the lines of the element under study are given the same intensity; the concentration of the element being determined is calculated from the ratio of the values of the cuttings. 2) is similar, but with one spark gap (Fig. 17).

Light from F is divided into two beams and passes through sectors S 1 and S 2, using the Hüfner rhombus R, two strips of the spectrum are obtained one above the other; Sp - spectrograph slit. The sector cuts are changed until the intensity of the impurity line and any nearby line of the main substance are equal, and the percentage content of the element being determined is calculated from the ratio of the cut values. 3) When used as a photometer rotating logarithmic sector the lines take on a wedge-shaped appearance on the spectrograms. One of these sectors and its position relative to the spectrograph during operation is shown in Fig. 18, a and b.

The sector cutting obeys the equation

- log Ɵ = 0.3 + 0.2l

where Ɵ is the length of the arc in parts of a full circle, located at a distance I, measured in mm along the radius from its end. A measure of the intensity of the lines is their length, since with a change in the concentration of an element, the length of its wedge-shaped lines also changes. First, using samples with known content, a diagram is constructed of the dependence of the length of a line on the % content; When analyzed on a spectrogram, the length of the same line is measured and the percentage is found from the diagram. There are several different modifications of this method. It is worth pointing out the modification of Scheibe, who used the so-called. double logarithmic sector. A view of this sector is shown in Fig. 19.

The lines are then examined using a special apparatus. Accuracy achievable using logarithmic sectors, ±(10-15)%; Scheibe's modification gives an accuracy of ±(5-7)%. 4) Quite often, photometry of spectral lines is used using light and thermoelectric spectrophotometers of various designs. Thermoelectric photometers, designed specifically for the purpose of quantitative analysis, are convenient. For example in FIG. Figure 20 shows a diagram of the photometer according to Sheibe:

L is a constant light source with a condenser K, M is a photographic plate with the spectrum being studied, Sp is a slit, O 1 and O 2 are lenses, V is a shutter, Th is a thermoelement that is connected to the galvanometer. A measure of the intensity of the lines is the deflection of the galvanometer needle. Less commonly used are self-registering galvanometers, which record the intensity of lines in the form of a curve. The analysis accuracy when using this type of photometry is ±(5-10)%. When combined with other methods of quantitative analysis, the accuracy may be increased; for example, three line method Scheibe and Schnettler, which is a combination of the homologous pair method and photometric measurements, in favorable cases can give an accuracy of ±(1-2)%.

Ministry of Education and Science
Republic of Kazakhstan

Karaganda State University
named after E.A. Buketova

Faculty of Physics

Department of Optics and Spectroscopy

Course work

on the topic of:

Spectra. WITH spectral analysis and its application.

Prepared by:

student of the FTRF-22 group

Akhtariev Dmitry.

Checked:

teacher

Kusenova Asiya Sabirgalievna

Karaganda - 2003 Plan

Introduction

1. Energy in the spectrum

2. Types of spectra

3. Spectral analysis and its application

4. Spectral devices

5. Spectrum of electromagnetic radiation

Conclusion

List of used literature

Introduction

Studying the line spectrum of a substance allows us to determine what chemical elements it consists of and in what quantity each element is contained in a given substance.

The quantitative content of an element in the sample under study is determined by comparing the intensity of individual lines in the spectrum of this element with the intensity of the lines of another chemical element, the quantitative content of which in the sample is known.

Method for determining quality and quantitative composition The analysis of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in mineral exploration to determine the chemical composition of ore samples. In industry, spectral analysis makes it possible to control the composition of alloys and impurities introduced into metals to obtain materials with specified properties.

The advantages of spectral analysis are high sensitivity and speed of obtaining results. Using spectral analysis, it is possible to detect the presence of gold in a sample weighing 6 * 10 -7 g with its mass of only 10 -8 g. Determination of the steel grade by the method of spectral analysis can be performed in a few tens of seconds.

Spectral analysis allows you to determine chemical composition celestial bodies, distant from Earth at distances of billions of light years. The chemical composition of the atmospheres of planets and stars, cold gas in interstellar space is determined from absorption spectra.

By studying the spectra, scientists were able to determine not only the chemical composition of celestial bodies, but also their temperature. By the displacement of spectral lines, one can determine the speed of movement of a celestial body.

Energy in the spectrum.

The light source must consume energy. Light is electromagnetic waves with a wavelength of 4*10 -7 - 8*10 -7 m. Electromagnetic waves emitted by the accelerated movement of charged particles. These charged particles are part of atoms. But without knowing how the atom is structured, nothing reliable can be said about the radiation mechanism. It is only clear that there is no light inside an atom, just as there is no sound in a piano string. Like a string that begins to sound only after being struck by a hammer, atoms give birth to light only after they are excited.

In order for an atom to begin to radiate, energy must be transferred to it. When emitting, an atom loses the energy it receives, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary.

Thermal radiation. The simplest and most common type of radiation is thermal radiation, in which the energy lost by atoms to emit light is compensated by the energy of thermal motion of atoms or (molecules) of the emitting body. The higher the body temperature, the faster the atoms move. When fast atoms (molecules) collide with each other, part of their kinetic energy is converted into excitation energy of the atoms, which then emit light.

The thermal source of radiation is the Sun, as well as an ordinary incandescent lamp. The lamp is a very convenient, but low-cost source. Only about 12% of the total energy released in the lamp electric shock, is converted into light energy. The thermal source of light is a flame. Grains of soot heat up due to the energy released during fuel combustion and emit light.

Electroluminescence. The energy needed by atoms to emit light can also come from non-thermal sources. During a discharge in gases, the electric field imparts greater kinetic energy to the electrons. Fast electrons experience collisions with atoms. Part of the kinetic energy of electrons goes to excite atoms. Excited atoms release energy in the form of light waves. Due to this, the discharge in the gas is accompanied by a glow. This is electroluminescence.

Cathodoluminescence. Glow solids, caused by bombardment by their electrons, is called cathodoluminescence. Thanks to cathodoluminescence, the screens of cathode ray tubes of televisions glow.

Chemiluminescence. For some chemical reactions, coming with the release of energy, part of this energy is directly spent on the emission of light. The light source remains cool (it is at ambient temperature). This phenomenon is called chemioluminescence.

Photoluminescence. Light incident on a substance is partially reflected and partially absorbed. The energy of absorbed light in most cases only causes heating of bodies. However, some bodies themselves begin to glow directly under the influence of radiation incident on them. This is photoluminescence. Light excites the atoms of a substance (increases their internal energy), after which they are illuminated themselves. For example, the luminous paints that cover many Christmas tree decorations emit light after being irradiated.

The light emitted during photoluminescence, as a rule, has a longer wavelength than the light that excites the glow. This can be observed experimentally. If you direct a light beam passed through a violet filter onto a vessel with fluoresceite (an organic dye), then this liquid begins to glow with green-yellow light, i.e. light of a longer wavelength than violet light.

The phenomenon of photoluminescence is widely used in fluorescent lamps. Soviet physicist S.I. Vavilov proposed covering inner surface discharge tube with substances capable of glowing brightly under the action of short-wave radiation from a gas discharge. Fluorescent lamps are approximately three to four times more economical than conventional incandescent lamps.

The main types of radiation and the sources that create them are listed. The most common sources of radiation are thermal.

Energy distribution in the spectrum. None of the sources produces monochromatic light, that is, light of a strictly defined wavelength. We are convinced of this by experiments on the decomposition of light into a spectrum using a prism, as well as experiments on interference and diffraction.

The energy that light carries with it from the source is distributed in a certain way over the waves of all lengths that make up the light beam. We can also say that energy is distributed over frequencies, since there is a simple relationship between wavelength and frequency: ђv = c.

Flux density electromagnetic radiation, or intensity /, is determined by the energy &W attributable to all frequencies. To characterize the frequency distribution of radiation, it is necessary to introduce a new quantity: the intensity per unit frequency interval. This quantity is called the spectral density of radiation intensity.

The spectral radiation flux density can be found experimentally. To do this, you need to use a prism to obtain the radiation spectrum, for example, of an electric arc, and measure the radiation flux density falling on small spectral intervals of width Av.

You cannot rely on your eye to estimate energy distribution. The eye has selective sensitivity to light: its maximum sensitivity lies in the yellow-green region of the spectrum. It is best to take advantage of the property of a black body to almost completely absorb light of all wavelengths. In this case, radiation energy (i.e. light) causes heating of the body. Therefore, it is enough to measure the body temperature and use it to judge the amount of energy absorbed per unit time.

An ordinary thermometer is too sensitive to be successfully used in such experiments. More sensitive instruments are needed to measure temperature. You can take an electric thermometer, in which the sensitive element is made in the form of a thin metal plate. This plate must be covered thin layer soot, which almost completely absorbs light of any wavelength.

The heat-sensitive plate of the device should be placed in one or another place in the spectrum. The entire visible spectrum of length l from red to violet rays corresponds to the frequency interval from v cr to y f. The width corresponds to a small interval Av. By heating the black plate of the device, one can judge the radiation flux density per frequency interval Av. Moving the plate along the spectrum, we will find that most of the energy is in the red part of the spectrum, and not in the yellow-green, as it seems to the eye.

Based on the results of these experiments, it is possible to construct a curve of the dependence of the spectral density of radiation intensity on frequency. The spectral density of radiation intensity is determined by the temperature of the plate, and the frequency is not difficult to find if the device used to decompose the light is calibrated, that is, if it is known what frequency a given part of the spectrum corresponds to.

By plotting along the abscissa axis the values of the frequencies corresponding to the midpoints of the intervals Av, and along the ordinate axis the spectral density of the radiation intensity, we obtain a number of points through which we can draw a smooth curve. This curve gives a visual representation of the distribution of energy and the visible part of the spectrum of the electric arc.

Since the discovery of “spectral analysis,” there has been much controversy surrounding this term. At first physical principle spectral analysis implied a method of identification elemental composition samples according to the observed spectrum, which was excited in some high-temperature flame source, spark or arc.

Later, spectral analysis began to be understood as other methods of analytical study and excitation of spectra:

Raman scattering methods,
absorption and luminescence methods.

Eventually, X-ray and gamma spectra were discovered. Therefore, it is correct, when speaking about spectral analysis, to mean the totality of all existing methods. However, more often the phenomenon of identification by spectra is used in understanding emission methods.

Classification methods

Another classification option is the division into molecular (determining the molecular composition of a sample) and elementary (determining the atomic composition) studies of spectra.

The molecular method is based on the study of absorption, Raman scattering and luminescence spectra; the atomic composition is determined from excitation spectra in hot springs (molecules are mainly destroyed) or from X-ray spectral studies. But such a classification cannot be strict, because sometimes both of these methods coincide.

Classification of spectral analysis methods

Based on the problems that are solved by the methods described above, the study of spectra is divided into methods used to study alloys, gases, ores and minerals, finished products, pure metals etc. Each studied object has its own characteristic features and standards. Two main directions of spectrum analysis:

Qualitative
Quantitative

What is studied during them, we will consider further.

Diagram of spectral analysis methods

Qualitative spectral analysis

Qualitative analysis serves to determine what elements the analyzed sample consists of. It is necessary to obtain the spectrum of a sample excited in some source, and from the detected spectral lines to determine which elements they belong to. This will make it clear what the sample consists of. The difficulty of qualitative analysis is the large number of spectral lines on the analytical spectrogram, the decoding and identification of which is too labor-intensive and inaccurate.

Quantitative spectral analysis

The method of quantitative spectral analysis is based on the fact that the intensity of the analytical line increases with increasing content of the element being determined in the sample. This dependence is based on many factors that are difficult to calculate numerically. Therefore, it is practically impossible to theoretically establish a relationship between line intensity and element concentration.

Therefore, relative measurements intensities of the same spectral line when the concentration of the element being determined changes. Thus, if the conditions of excitation and recording of spectra remain unchanged, the measured radiation energy is proportional to the intensity. Measuring this energy (or a value dependent on it) gives us the empirical connection we need between the measured value and the concentration of the element in the sample.

Spectral analysis

Spectral analysis- a set of methods for qualitative and quantitative determination of the composition of an object, based on the study of the spectra of interaction of matter with radiation, including the spectra of electromagnetic radiation, acoustic waves, distribution of masses and energies of elementary particles, etc.

Depending on the purposes of analysis and the types of spectra, several methods of spectral analysis are distinguished. Atomic And molecular spectral analyzes make it possible to determine the elemental and molecular composition of a substance, respectively. In the emission and absorption methods, the composition is determined from the emission and absorption spectra.

Mass spectrometric analysis is carried out using the mass spectra of atomic or molecular ions and allows one to determine the isotopic composition of an object.

Story

Dark lines on spectral stripes have been noticed for a long time, but the first serious research these lines were only undertaken in 1814 by Joseph Fraunhofer. In his honor, the effect was called “Fraunhofer lines”. Fraunhofer established the stability of the positions of the lines, compiled a table of them (he counted 574 lines in total), and assigned an alphanumeric code to each. No less important was his conclusion that the lines are not associated with either the optical material or the earth’s atmosphere, but are natural characteristic sunlight. He discovered similar lines in artificial light sources, as well as in the spectra of Venus and Sirius.

It soon became clear that one of the clearest lines always appeared in the presence of sodium. In 1859, G. Kirchhoff and R. Bunsen, after a series of experiments, concluded: each chemical element has its own unique line spectrum, and from the spectrum of celestial bodies one can draw conclusions about the composition of their substance. From this moment on, spectral analysis appeared in science, a powerful method for remote determination of chemical composition.

To test the method in 1868, the Paris Academy of Sciences organized an expedition to India, where a complete solar eclipse. There, scientists discovered: all the dark lines at the moment of the eclipse, when the emission spectrum replaced the absorption spectrum of the solar corona, became, as predicted, bright against a dark background.

The nature of each of the lines and their connection with chemical elements were gradually clarified. In 1860, Kirchhoff and Bunsen discovered cesium using spectral analysis, and in 1861, rubidium. And helium was discovered on the Sun 27 years earlier than on Earth (1868 and 1895, respectively).

Principle of operation

The atoms of each chemical element have strictly defined resonant frequencies, as a result of which it is at these frequencies that they emit or absorb light. This leads to the fact that in a spectroscope, lines (dark or light) are visible on the spectra in certain places characteristic of each substance. The intensity of the lines depends on the amount of substance and its state. In quantitative spectral analysis, the content of the substance under study is determined by the relative or absolute intensities of lines or bands in the spectra.

Optical spectral analysis is characterized by relative ease of implementation, the absence of complex sample preparation for analysis, and a small amount of substance (10-30 mg) required for analysis big number elements.

Atomic spectra (absorption or emission) are obtained by transferring the substance into a vapor state by heating the sample to 1000-10000 °C. A spark or an alternating current arc are used as sources of excitation of atoms in the emission analysis of conductive materials; in this case, the sample is placed in the crater of one of the carbon electrodes. Flames or plasmas of various gases are widely used to analyze solutions.

Application

IN Lately, greatest distribution obtained emission and mass spectrometric methods of spectral analysis based on the excitation of atoms and their ionization in argon plasma of induction discharges, as well as in a laser spark.

Spectral analysis is a sensitive method and is widely used in analytical chemistry, astrophysics, metallurgy, mechanical engineering, geological exploration and other branches of science.

In signal processing theory, spectral analysis also means the analysis of the energy distribution of a signal (for example, audio) over frequencies, wave numbers, etc.